Replication of Nondefective Parvoviruses: Lack of a Virion-Associated DNA Polymerase

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Abstract
Four of the nondefective parvoviruses were examined for an associated DNA polymerase. Virions were purified from neuraminidase-treated infected-mammalian cell lysates by isopycnic centrifugation in CsCl or from infected cell material by CaCl2 precipitation and centrifugation through sucrose into CsCl. Preparations of bovine parvovirus or Kilham rat virus obtained by the former procedure contained DNA polymerase activity but were not free of contaminating cellular proteins. The latter method produced viral preparations free of contaminating cellular proteins, and no DNA polymerase activity was detected in light infectious particles of H-1, LuIII, bovine parvovirus or Kilham rat virus. Examination of levels of each cellular DNA polymerase in these preparations from each step of both purification procedures revealed that DNA polymerase .beta. had a greater tendency to copurify with bovine parvovirus and Kilham rat virus than did DNA polymerases .alpha. or .gamma.. Disruption of infectious virions obtained by the 2nd purification method with detergents and sonic treatment did not result in the detection of a DNA polymerase activity. The biological activity and purity of each of the 4 different viruses obtained by the latter procedure were determined by hemagglutination and infectivity assays, polyacrylamide gel electrophoresis, and EM. In each case, the virions banding at a density of 1.39-1.41 g/cm2 in CsCl were infectious and contained only the virion structural proteins. DNA polymerase activity was not detected in any of these preparations, apparently indicating that a virion-associated DNA polymerase is not required for productive infection with the nondefective parvoviruses.

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